EP 1 447 250 A2 describes a filter system comprising a filter insert that is accommodated in a filter housing and comprises two plate-shaped individual filters, which are designed separately from each other and positioned adjacent to each other. The individual filters each have a rectangular shape; however, they have differing sizes and are accommodated in the filter housing with a vertical offset. The fluid to be purified flows through the filter elements orthogonally to the respective filter plane of the same.
DE 198 16 431 A1 describes a filter element for an air filter which is designed as a filter bellows having zigzag pleating, wherein the filter bellows has various pleat regions in which the pleat heights and/or the direction of the pleats differ from each other. The air to be purified flows through the filter bellows orthogonally to the filter plane of the same, wherein the incident flow side has a stepped design due to the differing heights of the various regions, while the clean sides of all filter regions are located in a common plane.